A special optical observation technique, such as narrow band imaging (NBI) and blue laser imaging (BLI), that facilitates detection of lesions is known. Observation according to this technique involves irradiating a observation site with narrow band light and imaging the light reflected therefrom. In white light imaging, an endoscope that uses an image sensor equipped with color filters arranged in a primary color Bayer array is used to enable simultaneous observation while maintaining excellent color reproduction.
According to this special optical observation technique, information that has entered B pixels significantly contributes to imaging of capillaries and thus B pixel information is mainly used in the display. When such observation is performed by using color filters arranged in a primary color Bayer array in which B pixels account for only one quarter of all pixels, the resolution of capillaries is insufficient.
Also known is a technique that uses G pixels having a sub-sensitivity range of the B range so that the B range information can also be obtained through G pixels. According to this technique, B information is extracted from the G pixels through image processing (for example, refer to PTL 1).